Heterogeneity in dose distribution in Yttrium-90 and Holmium-166 microspheres radioembolization of hepatic tumors

Nuclear medicine therapies face challenges in dosimetric control related to the patient's anatomy, metabolism, and limitations in dose estimation methods. These challenges are amplified by the introduction of new radio- pharmaceuticals and technologies, particularly in the field of theranostics. In this work, the spatial dosimetric heterogeneity generated by microspheres used in radioembolization was characterized and compared as a function of radial position in singular conformations and around clusters. The Monte Carlo simulation package PENELOPE 2014 was used to simulate absorbed doses in homogeneous liver tissue generated by the main microspheres available for treatment: glass- 90Y, resin- 90Y, and PLLA- 166Ho. It was determined the parameters of Russel's equation that better describe the absorbed dose per initial activity of this microspheres, updating the constants for 90Y, and determining them to 166Ho. At a radial distance of 0.77 cm from the center of the microspheres, 90Y microspheres provide an absorbed dose per initial activity 126 times greater than 166Ho microspheres. At this same depth, Y-90 absorbed dose generated by glass and resin microspheres shows a maximum difference of 4%. For clusters, an increased level of dose per initial activity was observed in the vicinity of all median clusters (around 340 mu m diameter). The results of this study highlight the spatial dosimetric heterogeneity and its significant dependence on the choice of microsphere type, emphasizing the considerable impact often neglected in therapeutic planning worldwide.